In a speed control of a synchronous motor, a conversion coefficient that expresses a relationship between a torque command and actual torque that is actually output from the motor is generally called a torque constant. In general, the torque constant is a fixed value that does not change with speed or current and configures a speed control system. However, the actual torque constant is not always fixed. The torque constant may not be fixed due to an influence of current flowing in the motor and a current control circuit.
PTL1 discloses a conventional method as a technical measure to cope with it. PTL1 has a means to measure actual output torque relative to the torque command by actually driving the motor, and correct the torque command. PTL1 controls the motor using this corrected torque command, so as to keep a fixed torque constant.
However, the above conventional method can correct the torque constant according to motor specifications, but cannot correct an influence of individual differences, such as variation in motor production and variation in characteristic of electronic components in a drive circuit.